3D printed hyperelastic "bone" scaffolds and regional gene therapy: A novel approach to bone healing

Abstract

The purpose of this study was to evaluate the viability of human adipose-derived stem cells (ADSCs) transduced with a lentiviral (LV) vector to overexpress bone morphogenetic protein-2 (BMP-2) loaded onto a novel 3D printed scaffold. Human ADSCs were transduced with a LV vector carrying the cDNA for BMP-2. The transduced cells were loaded onto a 3D printed Hyperelastic "Bone" (HB) scaffold. In vitro BMP-2 production was assessed using enzyme-linked immunosorbent assay analysis. The ability of ADSCs loaded on the HB scaffold to induce in vivo bone formation in a hind limb muscle pouch model was assessed in the following groups: ADSCs transduced with LV-BMP-2, LV-green fluorescent protein, ADSCs alone, and empty HB scaffolds. Bone formation was assessed using radiographs, histology and histomorphometry. Transduced ADSCs BMP-2 production on the HB scaffold at 24 hours was similar on 3D printed HB scaffolds versus control wells with transduced cells alone, and continued to increase after 1 and 2 weeks of culture. Bone formation was noted in LV-BMP-2 animals on plain radiographs at 2 and 4 weeks after implantation; no bone formation was noted in the other groups. Histology demonstrated that the LV-BMP-2 group was the only group that formed woven bone and the mean bone area/tissue area was significantly greater when compared with the other groups. 3D printed HB scaffolds are effective carriers for transduced ADSCs to promote bone repair. The combination of gene therapy and tissue engineered scaffolds is a promising multidisciplinary approach to bone repair with significant clinical potential. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1104-1110, 2018.

Keywords: 3D printing; bone; gene therapy; scaffold; tissue engineering.

FIGURE 1.

A: Image of the HB 3D printed scaffold after completion of the fabrication process. B: Cross-sectional image demonstrating the high porosity of the scaffold with open channels at each end to facilitate vascular ingrowth and bone formation.

FIGURE 2.

Plain radiographs taken at 2 weeks after implantation of ADSCs on the HB scaffold or HB scaffold alone in a hind limb muscle pouch. There is evidence of robust bone formation (white arrow) in the group implanted with ADSCs transduced with a LV carrying the cDNA for BMP-2 (group I, top left). There is no evidence of bone formation in groups II–IV (group II- ADSC/LV-GFP 1 HB Scaffold, group III- Nontransduced ADSC + HB Scaffold, group IV–HB Scaffold Alone).

FIGURE 3.

20× histology images stained with MT. The histological slices represent the same area of each muscle pouch at the interface between the exterior of the HB scaffold and native muscle. In group I there is evidence of woven bone formation (yellow arrow). There is no evidence of bone formation in groups II–IV.

FIGURE 4.

Histomorphometry calculations of average BA to TA ratios between the four animal groups. The error bars represent the upper and lower limits of the BA/TA ratio among the five animals in each group. The BA/TA ratio was significantly greater in group I compared with groups II–IV (p = 0.002). (group I- ADSC/LV-BMP-2 + HB Scaffold, group II- ADSC/LV-GFP + HB Scaffold, group III- Nontransduced ADSC + HB Scaffold, group IV- HB Scaffold Alone).